Category: Here comes the BOOM!
While it not be the largest, or the biggest, this is by far one of my favorite explosions in the Star Wars Saga. In Episode Two, four SPHA-T artillery batteries fire massive beam lasers at a Droid starship, causing several small explosions until one battery hits a sweet spot, causing a massive explosion (shown in the MOC) that brings down the starship. Unfortunately, I only had time to edit the main pic and remove my desk because I have a Calculus AP exam tomorrow. Please forgive the messy background!
http://www.flickr.com/photos/thebeetle/sets/72157633430335577/